The broad goals of this proposal are to determine the roles for integrin receptors in the development and function of T-lymphocytes. A combination of in vivo and in vitro approaches have been chosen. In order to test the role of integrin receptor function in T cell development, transgenic mice have been produced with a dominant negative form of integrin. Specifically, this laboratory is using a construct with the active integrin beta 1 cytoplasmic domain connected to the extracellular domain of the tac antigen, which breaks the transmembrane connection between extracellular matrix and the cytoskeleton provided by integrin receptors. The proximal lck promoter has been chosen to direct thymic specific expression of this construct in transgenic mice, leading to a reduction in the number of mature, single positive thymocytes in these mice as compared to normal liftermates. Our hypothesis is that this deficit represent a lack of positive selection in the transgenic mice, and we will test that hypothesis using transgenic mice with monoallelic expression of a T cell receptor (TCR) with a defined antigen recognition. Depending on the genetic background, conditions can be established in which mature thymocytes are produced only by positive selection of the monoallelic clones. Since positive selection has been shown to require p2lras, transgenic mice expressing a dominant negative form of the adaptor protein Shc will be produced, which should block integrin signaling to p21 ras. In vitro, molecular approaches to dissect integrin signaling pathways in co-stimulatory function of T cells will be done. Using recently developed reporter constructs, the role of versus FAK activation in of the TCR integrins have in co-stimulation on selected ECM substratum, and the role this signaling could play in chronic inflammatory diseases.